The present invention relates to a needle holder assembly for use with a medical administering device or appliance such as a hypodermic syringe or a venoclysis equipment for introducing a liquid medicament or transfusing blood into human body.
Extreme precautions are taken to prevent a pharmaceutical preparation or blood for transfusion from becoming contaminated with impurities before the preparation or blood is injected into the human body. Actually, however, there still exist various possibilities that impurities are present in or admixed to the preparation or blood before and even during the administering process. Impurities may happen to be introduced into a liquid medicament when, for example, an ampoule or other breakable container storing the preparation is punctured prior to injection or when a fluid conducting tube is being fitted to the rubber plug of the reservoir of a venoclysis equipment. The fine fragments of the punctured container or the fine particles of rubber scrapped off from the plug of the venoclysis equipment may find their way through the administering system into the blood stream of the human body and may thus injure the vascular tissues.
A variety of filter media have therefore been developed and have found practical applications for the purpose of removing impurities from liquid medicaments and blood for transfusion before the medicaments or blood are discharged from the needles of canulae of the administering devices. One of the typical examples of the prior art filter media adapted to achieve this purpose if formed of staple fibers which are pressed or otherwise compacted into lump form and another example if formed of nylon fabrics or a mass of sintered nylon powder. The filter element is usually fitted into the passageway in the needle holder and collects impurities when the liquid medicament or blood for transfusion is passed through the filter element toward the needle. When the filter element is thus subjected to the stream of the medicament of blood passing therethrough, it frequently happens that relatively short fibers or the fragments of fibers are separated from the lump of the compacted staple fibers or the fabrics of nylon or fine gragments are fractured or torn apart from the mass of the sintered nylon powder. This not only results in deterioration of the collection efficiency of the filter element being used but is causative of production of additional impurities (herein called "secondary impurities") although the majority of the impurities (herein called "primary impurities") initially contained in the medicament or blood directed into the needle holder may be collected by the filter element. The filter element thus provides in itself another source of impurities and loses in significance as the filter means.
With a view to solving these problems, I, the inventor, have proposed a new filter element in a medical needle assembly as disclosed in U.S. Pat. No. 3,859,999 dated Jan. 14, 1975 and assigned to Ishikawa Manufacturing Company, Limited, Tokyo, Japan. The filter element shown in this issued patent comprises a wad of at least one length of continuous filament of synthetic resin substantially uniformly entwined into wad form and is preferably located at the foremost end of the longitudinal passageway in a needle holder. In the course of the manufacture of such needle assemblies on a commercial basis, however, it has been found that difficulties are encountered in accurately locating the filter element in the needle holder and fixedly holding the filter element in position within the needle holder. This is partly because of the extremely small space available in the needle holder and partly because of the inherently shapeless configuration of the filter element composed of the wad of an entwined filament. If the filter element is located off of a predetermined position relative to the needle holder or dislodged from the predetermined position, the filter element causes obstruction when the needle assembly is being fitted to a syringe barrel or an adapter of a venoclysis equipment. The present invention contemplates provision of a medical needle holder assembly which is free from such a problem encountered in the applicant's previously proposed needle assembly as well as the problems inherent in needle holder assemblies using other prior art filter elements of the natures hereinbefore described.